Dynamic stabilization connecting member with slitted core and outer sleeve

ABSTRACT

A dynamic fixation medical implant having at least two bone anchors includes a longitudinal connecting member assembly having an elongate core and an outer sleeve. The core may be substantially cylindrical, of one-piece construction, and includes end portions for attachment to the bone anchors. A portion of the core extending between the bone anchors has at least one slit. The outer sleeve may include compression grooves. The sleeve surrounds the core and extends between the pair of bone anchors, the sleeve being compressible in a longitudinal direction between the bone anchors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/850,464 filed Oct. 10, 2006, the disclosure of which is incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 11/522,503, filed Sep. 14, 2006 that claims the benefit of U.S. Provisional Application Nos. 60/722,300, filed Sep. 30, 2005; 60/725,445, filed Oct. 11, 2005; 60/728,912, filed Oct. 21, 2005; 60/736,112, filed Nov. 10, 2005, and 60/832,644, filed Jul. 21, 2006; the disclosures all of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for use in bone surgery, particularly spinal surgery, and in particular to longitudinal connecting members and cooperating bone anchors or fasteners for such assemblies, the connecting members being attached to at least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that are placed in fixed relation by the installation therealong of bone screws or other bone anchors and cooperating longitudinal connecting members or other elongate members. Fusion results in the permanent immobilization of one or more of the intervertebral joints. Because the anchoring of bone screws, hooks and other types of anchors directly to a vertebra can result in significant forces being placed on the vertebra, and such forces may ultimately result in the loosening of the bone screw or other anchor from the vertebra, fusion allows for the growth and development of a bone counterpart to the longitudinal connecting member that can maintain the spine in the desired position even if the implants ultimately fail or are removed. Because fusion has been a desired component of spinal stabilization procedures, longitudinal connecting members have been designed that are of a material, size and shape to largely resist flexure, extension, torsion, distraction and compression, and thus substantially immobilize the portion of the spine that is to be fused. Thus, longitudinal connecting members are typically uniform along an entire length thereof, and usually made from a single or integral piece of material having a uniform diameter, width or cross-sectional area of a size to provide substantially rigid support in all planes with varying degrees of rigidity.

Fusion, however, has some undesirable side effects. One apparent side effect is the immobilization of a portion of the spine. Furthermore, although fusion may result in a strengthened portion of the spine, it also has been linked to more rapid degeneration and even hyper-mobility and collapse of spinal motion segments that are adjacent to the portion of the spine being fused, reducing or eliminating the ability of such spinal joints to move in a more normal relation to one another. In certain instances, fusion has also failed to provide pain relief.

An alternative to fusion and the use of more rigid longitudinal connecting members or other rigid structure has been a “soft” or “dynamic” stabilization approach in which a flexible loop-, S-, C- or U-shaped member or a coil-like and/or a spring-like member is utilized as an elastic longitudinal connecting member fixed between a pair of pedicle screws in an attempt to create, as much as possible, a normal loading pattern between the vertebrae in flexion, extension, distraction, compression, side bending and torsion. Problems may arise with such devices, however, including soft tissue ingrowth with scarring, lack of adequate spinal support and lack of fatigue strength or endurance limit. Fatigue strength has been defined as the repeated loading and unloading of a specific stress on a material structure until it fails. Fatigue strength can be tensile or distraction, compression, shear, torsion, bending, or a combination of these.

Another type of soft or dynamic system known in the art includes bone anchors connected by flexible cords or strands, typically made from a synthetic material. Such a cord or strand may be threaded through cannulated spacers that are disposed between adjacent bone anchors when such a cord or strand is implanted, tensioned and attached to the bone anchors. The spacers typically span the distance between bone anchors, providing limits on the bending movement of the cord or strand and thus strengthening and supporting the overall system. Such cord or strand-type systems require specialized bone anchors and tooling for tensioning and holding the chord or strand in the bone anchors. Although flexible, the cords or strands utilized in such systems do not allow for elastic distraction or stretchability of the system once implanted because the cord or strand must be stretched or pulled to maximum tension in order to provide a stable, supportive system.

The complex dynamic conditions associated with spinal movement therefore provide quite a challenge for the design of elongate elastic longitudinal connecting members that exhibit an adequate fatigue strength to provide stabilization and protected motion of the spine, without fusion, and allow for some natural movement of the portion of the spine being reinforced and supported by the elongate elastic or flexible connecting member. A further challenge are situations in which a portion or length of the spine requires a more rigid stabilization, possibly including fusion, while another portion or length may be better supported by a more dynamic system that allows for protected segmental spinal movement.

SUMMARY OF THE INVENTION

Longitudinal connecting member assemblies according to the invention for use between at least two bone anchors provide dynamic, protected motion of the spine and may be extended to provide additional dynamic sections or more rigid support along an adjacent length of the spine, with fusion, if desired. A longitudinal connecting member assembly according to the invention has an inner integral core or bar, a portion thereof having a slit. The slit is preferably helical. An outer sleeve or spacer surrounds the slitted portion of the core and is located entirely outside of a periphery of the slitted core or bar. In a preferred embodiment, the sleeve extends between a pair of adjacent bone anchors and has a cylindrical cross-sectional shape. The slitted core and outer sleeve cooperate dynamically, both features having some flexibility, with the outer sleeve primarily protecting and limiting flexing movement of the inner core. The outer sleeve may include a grooved portion that may be compressed upon installation between two bone anchors. As compared to dynamic systems that include flexible cords and spacers, embodiments according to the present invention advantageously allow for elastic distraction, elongation or stretchability of the connecting member assembly.

A variety of embodiments according to the invention are possible. For example, the inner core may extend between three or more bone anchors with some or all of the sections that are located between bone anchors having a slit and cooperating sleeve. Alternatively some of the sections may be of a more rigid construction and not include slits and sleeves.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, it is an object of the present invention to overcome one or more of the problems with bone attachment assemblies described above. An object of the invention is to provide dynamic medical implant stabilization assemblies having longitudinal connecting members that include an integral inner core having a flexible portion that allows for bending, torsion, compression and distraction of the assembly. Another object of the invention is to provide such an assembly wherein the flexible portion is insertable into a protective outer sleeve. A further object of the invention is to provide such an assembly wherein the outer sleeve is compressed upon installation, without having to directly tension the inner core, by compressing the bone anchors toward one another. A further object of the invention is to provide dynamic medical implant longitudinal connecting members that may be utilized with a variety of bone screws, hooks and other bone anchors. Another object of the invention is to provide a more rigid or solid connecting member portion or segment, if desired, such as a solid rod portion being integral with and adjacent to the core having the flexible portion. Additionally, it is an object of the invention to provide a lightweight, reduced volume, low profile assembly including at least two bone anchors and a longitudinal connecting member therebetween. Furthermore, it is an object of the invention to provide apparatus and methods that are easy to use and especially adapted for the intended use thereof and wherein the apparatus are comparatively inexpensive to make and suitable for use.

Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded front elevational view of a dynamic fixation connecting member assembly according to the invention including an inner core with a helical slit and an outer sleeve.

FIG. 2 is a front elevational view of a dynamic fixation assembly according to the invention including the connecting member assembly of FIG. 1 and two bone screws.

FIG. 3 is an enlarged and partial front elevational view of a portion of the inner core of FIG. 1.

FIG. 4 is an enlarged and partial cross-sectional view taken along the line 4-4 of FIG. 3.

FIG. 5 is an enlarged cross-sectional view of the inner core taken along the line 5-5 of FIG. 1.

FIG. 6 is an enlarged cross-sectional view of the outer sleeve taken along the line 6-6 of FIG. 1.

FIG. 7 is an exploded perspective view of the assembly of FIG. 2 showing the dynamic fixation connecting member, the two bone screws and a pair of closure structures.

FIG. 8 is a perspective view of the assembly of FIG. 7 shown fully assembled.

FIG. 9 is an enlarged cross-sectional view taken along the line 9-9 of FIG. 8.

FIG. 10 is a front elevational view of a second embodiment of an inner core according to the invention having a slitted portion and a solid portion.

FIG. 11 is a front elevational view of a second longitudinal connecting member assembly according to the invention having the inner core of FIG. 10, an outer sleeve cooperating with the slitted portion and three bone screws.

FIG. 12 is a front elevational view of a third embodiment of an inner core according to the invention having a pair of slitted portions.

FIG. 13 is a front elevational view of a third longitudinal connecting member assembly according to the invention having the inner core of FIG. 12, a pair of outer sleeves cooperating with the pair of slitted portions and three bone screws.

FIG. 14 is a front elevational view of a fourth embodiment of an inner core according to the invention having a pair of slitted portions and a solid portion.

FIG. 15 is a front elevational view of a fourth longitudinal connecting member assembly according to the invention having the inner core of FIG. 14, a pair of outer sleeves cooperating with the pair of slitted portions and four bone screws.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. It is also noted that any reference to the words top, bottom, up and down, and the like, in this application refers to the alignment shown in the various drawings, as well as the normal connotations applied to such devices, and is not intended to restrict positioning of the connecting member assemblies of the application and cooperating bone anchors in actual use.

With reference to FIGS. 1-9, the reference numeral 1 generally designates a non-fusion dynamic stabilization longitudinal connecting member assembly according to the present invention. The connecting member assembly 1 includes an inner core 8 and an outer sleeve or spacer 10. The inner core 8 is elongate, either linear or curvilinear, having a central longitudinal axis A and also including a first end portion or section 16 extending along the axis A, an opposite second end portion or section 18 and a mid-portion or section 20 having a helical slit 22. The inner core 8 is receivable in the flexible outer sleeve 10, with the sleeve 10 ultimately surrounding the slitted mid-portion 20 as will be described more fully below. The dynamic connecting member assembly 1 cooperates with at least a pair of bone anchors, such as the polyaxial bone screws, generally 25 and cooperating closure structures 27 shown in the drawings, the assembly 1 being captured and fixed in place at the end portions 16 and 18 by cooperation between the bone screws 25 and the closure structures 27. The sleeve 10 is sized and shaped to fit between pairs of bone screws 25 or other bone anchors, cooperating with the inner core 8 to support adjacent vertebrae. The sleeve 10 can be of any cross-sectional shape and can be cut to fit any needed length.

Because the end portions 16 and 18 are substantially solid and, in this illustrated embodiment, cylindrical, the connecting member assembly 1 may be used with a wide variety of bone anchors already available for cooperation with rigid rods including fixed, monoaxial bone screws, hinged bone screws, polyaxial bone screws, and bone hooks and the like, with or without compression inserts, that may in turn cooperate with a variety of closure structures having threads, flanges, or other structure for fixing the closure structure to the bone anchor, and may include other features, for example, break-off tops and inner set screws. The bone anchors, closure structures and the connecting member assembly 1 are then operably incorporated in an overall spinal implant system for correcting degenerative conditions, deformities, instabilities, injuries, or defects (congenital, developmental) to the spinal column of a patient. The end portions 16 and 18 can be of any length and the helical slit section can also vary in length.

The illustrated polyaxial bone screw 25 includes a shank 30 for insertion into a vertebra (not shown), the shank 30 being pivotally attached to an open receiver or head 31. The shank 30 includes a threaded outer surface and a central cannula or through-bore 32 disposed along an axis of rotation of the shank, the through-bore 32 extending between a top surface 33 and a bottom surface 34 of the shank 30. The bore 32 provides a passage through the shank interior for a length of wire or pin inserted into the vertebra prior to the insertion of the shank 30, the wire or pin providing a guide for insertion of the shank 30 into the vertebra.

The receiver 31 has a pair of spaced and generally parallel arms 35 that form an open generally U-shaped channel 37 therebetween that is open at distal ends of the arms 35. The arms 35 each include radially inward or interior surfaces 40 that have a discontinuous guide and advancement structure mateable with cooperating structure on the closure structure 27. In the illustrated embodiment, the guide and advancement structure is a partial helically wound flangeform configured to mate under rotation with a similar structure on the closure structure 27. However, it is foreseen that the guide and advancement structure could alternatively be a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structures for operably guiding under rotation and advancing the closure structure 27 downward between the receiver arms 35 and having such a nature as to resist splaying of the arms 35 when the closure 27 is advanced into the U-shaped channel 37.

Each of the arms 35 also includes a V-shaped or undercut tool engagement groove 41 formed on a substantially planar outer surface thereof which may be used for holding the receiver 31 with a holding tool (not shown) having projections that are received within the grooves 41 during implantation of the shank 30 into the vertebra (not shown). The grooves 41 may also cooperate with a holding tool during bone screw assembly and during subsequent installation of the connecting member assembly 1 and the closure structure 27. It is foreseen that tool receiving grooves or apertures may be configured in a variety of shapes and sizes and be disposed at other locations on the receiver arms 35.

The shank 30 and the receiver 31 may be attached in a variety of ways. For example, a spline capture connection as described in U.S. Pat. No. 6,716,214, and incorporated by reference herein, is shown in the drawing figures wherein the bone screw shank 30 includes a capture structure 42 mateable with a retaining structure 44 disposed within the receiver. The retaining structure 44 includes a partially spherical surface that is slidingly mateable with a cooperating inner surface of the receiver 31, allowing for a wide range of pivotal movement between the shank 30 and the receiver 31. Polyaxial bone screws with other types of capture connections may also be used according to the invention, including but not limited to, threaded connections, frictional connections utilizing frusto-conical or polyhedral capture structures, integral top or downloadable shanks, and the like. Also, as indicated above, polyaxial and other bone screws for use with connecting members of the invention may have bone screw shanks that attach directly to the connecting member or may include compression members or inserts that cooperate with the bone screw shank, receiver and closure structure to secure the connecting member assembly to the bone screw and/or fix the bone screw shank at a desired angle with respect to the bone screw receiver that holds the longitudinal connecting member assembly. Furthermore, although the closure structure 27 of the present invention is illustrated with the polyaxial bone screw 25 having an open receiver or head 31, it foreseen that a variety of closure structure may be used in conjunction with any type of medical implant having an open or closed head, including monoaxial bone screws, hinged bone screws, hooks and the like used in spinal surgery.

To provide a biologically active interface with the bone, the threaded shank 30 may be coated, perforated, made porous or otherwise treated. The treatment may include, but is not limited to a plasma spray coating or other type of coating of a metal or, for example, a calcium phosphate; or a roughening, perforation or indentation in the shank surface, such as by sputtering, sand blasting or acid etching, that allows for bony ingrowth or ongrowth. Certain metal coatings act as a scaffold for bone ingrowth. Bio-ceramic calcium phosphate coatings include, but are not limited to: alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca₃ (PO₄) 2 tetra-calcium phosphate (Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, is desirable as hydroxyapatite is chemically similar to bone with respect to mineral content and has been identified as being bioactive and thus not only supportive of bone ingrowth, but actively taking part in bone bonding.

The longitudinal connecting member assembly 1 illustrated in FIGS. 1-9 is elongate, with the inner core 8 being made from metal, metal alloys or other suitable materials, including plastic polymers such as polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes and composites. The outer sleeve or spacer 10 may be made of a variety of materials including metals, plastics and composites. The illustrated sleeve 10 is made from a plastic, such as a thermoplastic elastomer, for example, polycarbonate-urethane. In order to reduce the production of micro wear debris, that in turn may cause inflammation, it is desirable to make the inner core 8 from a different material than the sleeve 10. Additionally or alternatively, in order to result in adequate hardness and low or no wear debris, the sleeve 10 inner surfaces and cooperating core 8 outer surfaces may be coated with an ultra thin, ultra hard, ultra slick and ultra smooth coating, such as may be obtained from ion bonding techniques and/or other gas or chemical treatments.

Specifically, with the exception of the slitted mid portion 20, the illustrated core 8 is a substantially solid, smooth and uniform cylinder or rod having an outer cylindrical surface 50 and a circular cross-section. It is foreseen that in some embodiments, the core 8 may be substantially hollow, having a bore extending along the axis A all or part of an entire length of the core 8. The illustrated core 8 has an end 52 and an opposite end 54, with the solid end portion 16 terminating at the end 52 and the solid end portion 18 terminating at the end 54. The portions 16 and 18 are each sized and shaped to be received in the U-shaped channel 37 of a bone screw assembly 25 with the mid-portion 20 sized and shaped to extend between cooperating bone screws 25. It is foreseen that the core could be non-cylindrical in shape and in cross-section and that it can be cut to length to fit any clinical application.

With particular reference to FIGS. 3-5, the mid-portion 20 includes the helical slit 22 that is formed in and extends from the outer surface or periphery 50 toward the axis A. In the illustrated embodiment, a process of forming the helical slit 22 creates an aperture, inner space or bore 57 that extends along the axis A along a length L of the slit 22. In embodiments wherein the core 8 already has a through bore extending along the axis A, the helical slit extends through the outer surface 50 and an inner surface that defines such bore. The slit 22 disposed in part or all of the mid-portion 20, results in the mid-portion being coil- or spring-like in nature. Thus, when the core 8 is fixed to bone screws 25 at the end portions 16 and 18 thereof, the slitted mid-portion 20 provides relief (e.g., shock absorption) and limited movement with respect to flexion, extension, torsion, distraction and compressive forces placed on the assembly 1.

The sleeve 10 advantageously cooperates with the core helical slit 22 and is slidable thereon, providing limitation and protection of movement of the core 8 at the slit 22. The sleeve 10 also protects patient body tissue from damage that might otherwise occur in the vicinity of the helical slit 22. The sleeve 10 prevents soft tissue ingrowth into the slit 22 that could hinder the function of the slit 22. The sleeve 10 is sized and shaped for substantially even and precise alignment and substantial compressive contact between flat end surfaces 58 a and 58 b of the sleeve 10 and cooperating flat side surfaces 59 of the receivers 31. Furthermore, as will be discussed in greater detail below, when the sleeve is implanted, and the closure structures 27 are tightened, the tools utilized to implant the assembly 1 and/or the bone screws 27 are manipulated so as to axially compress the sleeve 10, now substantially coaxial with the core 8 axis A, between facing side surfaces 59 of adjacent receivers 31. Such pre-compression after installation results in some tension and distraction of the slitted mid-portion 20 of the core 8 when the implantation tools are removed from the bone screws 25, as the sleeve surfaces 58 a and 58 b then press against the facing bone screw surfaces 59, but the core 8 is otherwise fixed with respect to each of the bone screws 27 within the receiver channels 37. Such dynamic tension/compression relationship between the sleeve 10 and the slitted core 8 provides further strength and stability to the overall assembly and also allows for the entire connecting member assembly 1 to elongate, if needed, in response to spinal movement. The increased stability and strength of the assembly advantageously allows for use of a smaller, more compact, reduced volume, lower profile longitudinal connecting member assembly 1 and cooperating bone anchors than, for example, flexible cord and spacer type longitudinal connecting member assemblies. Also this type of assembly using a flexible non-cord like member allows the use of any type of bone anchor, polyaxial or not.

In the embodiment shown, the sleeve 10 is also substantially cylindrical with an external substantially cylindrical surface 60 and an internal substantially cylindrical and smooth surface 62. The surface 62 defines a bore 66 with a circular cross section, the bore 66 extending through the sleeve 10. In the illustrated embodiment, the sleeve 10 further includes a plurality of compression grooves 68. Sleeves according to the invention may include one, none or any desired number of grooves 68. Each of the illustrated grooves 68 is substantially uniform and circular in cross-section as illustrated in FIG. 6, being formed in the external surface 60 and extending radially toward the internal surface 62. The internal surface 62 is of a slightly greater diameter than an outer diameter of the cylindrical surface 50 of the core 8, allowing for axially directed sliding movement of the sleeve 10 with respect to the core 8. When the cylindrical core 8 is inserted in the sleeve 10, the sleeve 10 completely surrounds the helical slit 22. It is noted that in addition to limiting the bendability of the core 8 and thus providing strength and stability to the assembly 1, the sleeve 10 also keeps scar tissue from growing into the core 8 through the helical slit 22, thus eliminating the need for a sheath-like structure to be placed, adhered or otherwise applied to the core 8.

The core 8 may be sized and made from such materials as to provide for a relatively more rigid assembly 1 or a relatively more flexible assembly 1 with respect to flex or bendability along the assembly 1. Such flexibility therefore may be varied by changing the outer diameter of the core 8 and thus likewise changing the inner diametric size of the sleeve 10. Also, since the distance between the bone screw assembly receivers or heads can vary, the core 8 may need to be more or less stiff. The pitch of the helical slit 22 may also be varied to provide a more or less flexible core and the shock absorption desired. For example, it is noted that increasing the pitch (i.e., forming a more acute angle between the slant of the slit 22 with respect to the axis A results in a stiffer assembly with respect to bending and axial displacements. Furthermore, a benefit of increasing pitch is a lessening of impact loading between the surfaces defining the helical slit 22, thus dampening the jolts of an impact and improving shock absorption. Again the length of the slitted section can vary.

With reference to FIGS. 7-9, the closure structure 27 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the interior surface 40 of the upstanding arms 35 of the receiver 31. The illustrated closure structure 27 is rotatable between the spaced arms 35, but could be, for example, a slide-in closure structure or a ninety degree twist-in closure with opposed flange-like or wedge-like projections. The illustrated closure structure 27 is substantially cylindrical and includes an outer helically wound guide and advancement structure in the form of a flange form 76 that operably joins with the guide and advancement structure disposed on the interior 40 of the arms 35. The flange form 76 utilized in accordance with the present invention may take a variety of forms, including those described in Applicant's U.S. Pat. No. 6,726,689, which is incorporated herein by reference. It is also foreseen that according to the invention the closure structure guide and advancement structure could alternatively be a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structure for operably guiding under rotation and advancing the closure structure 27 downward between the arms 35 and having such a nature as to resist splaying of the arms 35 when the closure structure 27 is advanced into the U-shaped channel 37.

The illustrated closure structure 27 includes a lower surface 78 that is substantially planar and includes a point 80 and a rim 82 protruding therefrom for engaging the core 8 outer cylindrical surface at the non-slitted end portion 16 or 18. The closure structure 27 has a top surface 84 with an internal drive in the form of an aperture 86, illustrated as a star-shaped internal drive, for example, sold under the trademark TORX. A driving tool (not shown) sized and shaped for engagement with the internal drive 86 is used for both rotatable engagement and, if needed, disengagement of the closure 27 from the arms 35. Although a star-shaped internal drive 86 is shown in the drawings, the tool engagement structure may take a variety of forms and may include, but is not limited to, a hex shape or other features or apertures, such as slotted, tri-wing, spanner, two or more apertures of various shapes, and the like. It is also foreseen that the closure structure 27 may alternatively include a break-off head designed to allow such a head to break from a base of the closure at a preselected torque, for example, 70 to 140 inch pounds. Such a closure structure would also include a base having an internal drive to be used for closure removal.

In use, at least two bone anchor assemblies 25 are implanted into vertebrae for use with the longitudinal connecting member assembly 1. Each vertebra may be pre-drilled to minimize stressing the bone when screws are used. Furthermore, if and when a cannulated bone screw shank is utilized, each vertebra could have a guide wire or pin (not shown) inserted therein that is shaped for the bone screw cannula 32 of the bone screw shank 30 and provides a guide for the placement and angle of the shank 30 with respect to the cooperating vertebra. A further tap hole may be made and the shank 30 is then driven into the vertebra by rotation of a driving tool (not shown) that engages a driving feature near the top 33 of the shank 30 illustrated as a hex-shaped head. It is foreseen that the screws 25 and the longitudinal connecting member 1 can be inserted in a percutaneous or minimally invasive surgical manner.

With particular reference to FIG. 1, the longitudinal connecting member assembly 1 is assembled by inserting the core 8 into the bore 66 defined by the inner cylindrical surface 62 of the outer sleeve 10 after both the core 8 and the sleeve 10 have been cut to length. The end 54 of the core 8 is placed into the bore 66 at the surface 58 a and the sleeve 10 is moved toward the end portion 16 until the sleeve 10 is positioned between the end portions 16 and 18 and is disposed about the mid-portion 20, thus covering or encompassing the helical slit 22. It is noted that the core 8 and the sleeve 10 may also be assembled in other ways, for example, by inserting the end 52 of the core 8 into the sleeve 10 at the end surface 58 b. Furthermore, alignment of the slit 22 with respect to the grooves 68 along the axis A as shown, for example, in FIG. 2 is approximate and not intended to limit the relative position or location of the slit 22 with respect to the grooves 68 or the slit with respect to the pair of receivers 31. Such positioning may be determined, for example, in relation to a degree of overall flexibility desired for the assembly 1.

The connecting member assembly 1 is eventually positioned in an open or percutaneous manner in cooperation with the at least two bone anchors or screws 25 with the sleeve 10 disposed between the two bone screws 25 and the end portions 16 and 18 each within the U-shaped channels 37 of the two bone screws 25. Again, the end portions 16 and 18 could extend to other bone anchors. A closure structure 27 is then inserted into and advanced between the arms 35 of each of the bone anchor screws 25. The closure structure 27 is rotated, using a tool engaged with the inner drive 86 until a selected pressure is reached at which point the core 8 is urged toward, but not completely seated in the channel 37. For example, about 80 to about 120 inch pounds pressure may be required for fixing the bone screw shank 30 with respect to the receiver 31.

Downward movement of the closure structure 27 into the channel 37 presses a respective end portion 16 or 18 downward into engagement with a top 33 or other upper portion of the respective bone screw shank 30, pressing the respective retaining structure 44 into engagement with the respective receiver 31, thus setting an angle of articulation of the respective shank 30 with respect to the respective receiver 31, clamping the shank 30 into a fixed position with respect to the receiver 31. The receiver 31, the shank 30 and the retaining structure 44 cooperate in such a manner that the receiver 31 and the shank 30 can be secured at any of a plurality of angles, articulations or rotational alignments relative to one another and within a selected range of angles both from side to side and from front to rear, to enable flexible or articulated engagement of the receiver 31 with the shank 30 until both are locked or fixed relative to each other. Again it is also possible to use fixed or monoaxial screws with the invention, as described below.

Alternatively, it is foreseen that the capture of the connecting member assembly 1 by bone screws or other bone anchors and cooperating closure structures could further involve the use of an upper and/or a lower compression member or insert. Furthermore, the assembly 1 may cooperate with an open receiver that is integral or fixed in position with respect to a bone screw shank or bone hook, or with a receiver having limited angular movement with respect to the shank, such as a hinged connection, also with or without other compression members or inserts for fixing the assembly 1, the receiver and/or the bone anchor in a desired position or orientation with respect to the cooperating vertebrae.

As indicated previously herein, as the closure structures 27 are rotated and then tightened against the end portions 16 and 18 within a pair of spaced bone screws 25, such bone screws 25 may be pressed toward one another, thereby compressing and pre-loading the sleeve 10. When the insertion and tightening tools are removed, the resilient sleeve 10, pressing against facing surfaces 59 of the cooperating bone screw receivers 31, stretches and tensions the mid-portion 20 of the core 8 at the helical slit 22. The assembly 1 is thus substantially dynamically loaded and oriented relative to the cooperating vertebra, providing relief (e.g., shock absorption) and protected movement with respect to flexion, extension, torsional and distraction and compressive forces placed on the assembly 1 and the two connected bone screws 25. Again, the helical slit 22 allows the core 8 to twist or turn, providing relief for torsional stresses. The sleeve 10 can also limit such torsional movement as well as bending movement of the core 8, providing spinal support. Furthermore, because the sleeve 10 is compressed during installation, the sleeve advantageously allows for some protected extension or distraction of both the core 8 and the sleeve 10 as well as compression of the assembly 1 in cooperation with the core 8.

If removal of the assembly 1 from any of the bone screw assemblies 25 is necessary, or if it is desired to release the assembly 1 at a particular location, disassembly is accomplished by using the driving tool (not shown) with a star-shaped driving formation on the closure structure 27 internal drive 86 to rotate and remove the closure structure 27 from the receiver 31. Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly.

Eventually, if the spine requires more rigid support, the connecting member assembly 1 according to the invention may be removed and replaced with another longitudinal connecting member, such as a solid rod, having the same diameter as the inner core 8 end portions 16 and 18, utilizing the same receivers 31 and closure structures 27. Alternatively, if less support is eventually required, a less rigid, more flexible assembly, for example, an assembly 1 made of a more flexible material or an assembly 1 having a slit of different length and/or pitch, but with end portions having the same diameter as the inner core 8 end portions 16 and 18, may replace the assembly 1, also utilizing the same bone screws 25.

With reference to FIGS. 10 and 11, an alternative longitudinal connecting member assembly according to the invention, generally 101 includes an inner core 108 and an outer sleeve 110. The outer sleeve 110 is the same or substantially similar to the sleeve 10 previously described herein. The assembly 101 is shown attached to three bone screw assemblies 25, previously described herein, each bone screw assembly having a shank 30 and a receiver 31, also previously described herein. Although not shown, each bone screw assembly 25 further includes a closure structure 27, also previously described herein. As with the assembly 1, the assembly 101 readily cooperates with a wide variety of bone anchors and closures, also as previously described herein.

The connecting member assembly 101 is sized and shaped to attach to at least three bone screw assemblies 25, to provide a flexible dynamic stabilization length or segment 124 where the core 108 has a slit 122 and cooperates with the sleeve 110. The core length or segment 124 and the slit 122 are similar or nearly identical to the core 8 and sleeve 10, respectively, previously described herein. However, the segment 124 is integral or otherwise fixed to a more rigid length or segment 126 that is of solid construction and may be used in conjunction with spinal fusion along such length. The flexible length 124 that includes the slit 122 is disposed between the rigid length 126 and another shorter rigid length or portion 128 sized and shaped to be received by the third bone screw assembly 25. The sleeve 110 includes grooves 168 the same or substantially similar to the grooves 68 previously described herein with respect to the sleeve 10. Also, in the illustrated embodiment the portion 128 is substantially similar or identical to the end portion 16 previously described herein with respect to the core 8. It is noted that the portion 128 may also be elongate of any length, similar to the length 126, for cooperating with more than one bone anchor or bone screw assembly 25. Thus, an assembly 101 according to the invention may be used to provide protected movement of the spine along the segment 124, spinal fusion along the length 126 and spinal fusion on a length opposite the length 128, if the portion 128 is of sufficient length to attach to another bone screw assembly 25. It is noted that a portion or portions of the assembly 101 can be straight or curved, pre-bent or curvilinear.

In the illustrated embodiment, the portions or segments 124, 126 and 128 are integral and substantially uniform along a central longitudinal axis B thereof, and are cylindrical. The segments 124, 126 and 128 are also of solid construction with the exception of the portion of the segment 124 that has the helical slit 122. As indicated above, the helical slit 122 is similar or identical to the helical slit 22 previously described herein, having features and cross-sections as shown in FIGS. 3, 4 and 5.

In use, the assembly 101 is implanted in a manner substantially similar to that previously described herein with respect to the assembly 1. The segment 126 is ultimately located near a portion of the spine requiring more rigid support while the segment 124 and cooperating sleeve 110 are located near a portion of the spine requiring less support. If desired, during tightening of the closure structures 27 against the core 108, the sleeve 110 is compressed between facing bone screw receivers 31 as previously described herein with respect to the sleeve 10.

It is noted that an advantageous connecting member 101 according to the invention includes a rigid length or segment 126 made from a metal alloy that is elongate and intended for fusion along a major portion or section of the spine, for example, the rigid length 126 may be sized to extend from the sacrum to the thoracic spinal segment T10. Such an elongate portion or segment 126 is thus connectable to a plurality of bone anchors along the spine. Such a connecting member further includes a dynamic section 124 having a slit 122 and spacer or sleeve 110 that is sized for placement, for example, between T9 and T8. Such an embodiment is believed to minimize rapid degeneration and compressive fractures that tend to occur near ends of such elongate connecting member assemblies.

With reference to FIGS. 12 and 13, another alternative longitudinal connecting member assembly according to the invention, generally 201 includes an inner core 208 and two outer sleeves 210 a and 210 b. The outer sleeves 210 a and 210 b are the same or substantially similar to the sleeve 10 previously described herein. The assembly 201 is shown attached to three bone screw assemblies 25, previously described herein, each bone screw assembly having a shank 30 and a receiver 31, also previously described herein. Although not shown, each bone screw assembly 25 further includes a closure structure 27, also previously described herein. As with the assemblies 1 and 101, the assembly 201 readily cooperates with a wide variety of bone anchors and closures, also as previously described herein.

The connecting member assembly 201 is sized and shaped to attach to at least three bone screw assemblies 25, to provide two flexible dynamic stabilization lengths or segments 224 a and 224 b where the core 108 has respective slits 222 a and 222 b that cooperate with the respective sleeves 210 a and 210 b. The core lengths or segments 224 a and 224 b and the slits 222 a and 222 b are similar or nearly identical to the core 8 and sleeve 10, respectively, previously described herein. The illustrated segment 224 a is integral with the segment 224 b. The flexible length 224 a that includes the slit 222 a is integral or otherwise fixed to a rigid length 226. The flexible length 224 b that includes the slit 222 b is integral or otherwise fixed to a rigid length 228. In the illustrated embodiment, the lengths 226 and 228 are relatively short in length, being sized and shaped to be received by a receiver 31 of one of the bone screw assemblies 25. The sleeves 210 a and 210 b each include respective grooves 268 a and 268 b that are the same or substantially similar to the grooves 68 previously described herein with respect to the sleeve 10. Also, in the illustrated embodiment, the portions 226 and 228 are substantially similar or identical to the end portions 16 and 18 previously described herein with respect to the core 8. It is noted that the portions 226 and 228 may also be elongate, similar to the length 126 of the core 108, for cooperating with more than one bone screw assembly 25.

Thus the assembly 201 according to the invention is used to provide protected movement of the spine along both the segments 224 a and 225 b. In the illustrated embodiment, the portions or segments 224 a, 224 b, 226 and 228 are integral and substantially uniform along a central longitudinal axis C thereof, and are cylindrical. The segments 224 a, 224 b, 226 and 228 are also of solid construction with the exception of the portions of the segments 224 a and 224 b that have the respective helical slits 222 a and 222 b. As indicated above, the helical slits 222 a and 222 b are substantially similar or identical to the helical slit 22 previously described herein, having features and cross-sections as shown in FIGS. 3, 4 and 5.

In use, the assembly 201 is implanted in a manner substantially similar to that previously described herein with respect to the assembly 1. As with the assembly 1, if desired, during tightening of the closure structures 27 against the core 208, one or both of the sleeves 210 a and 210 b may be compressed between facing bone screw receivers 31 as previously described herein with respect to the sleeve 10.

With reference to FIGS. 14 and 15, another alternative longitudinal connecting member assembly according to the invention, generally 301 includes an inner core 308 and two outer sleeves 310 a and 310 b. The outer sleeves 310 a and 310 b are the same or substantially similar to the sleeve 10 previously described herein. The assembly 301 is shown attached to four bone screw assemblies 25, previously described herein, each bone screw assembly having a shank 30 and a receiver 31, also previously described herein. Although not shown, each bone screw assembly 25 further includes a closure structure 27, also previously described herein. As with the assemblies 1, 101 and 201, the assembly 301 readily cooperates with a wide variety of bone anchors and closures, also as previously described herein.

The connecting member assembly 301 is sized and shaped to attach to at least four bone screw assemblies 25, to provide two flexible dynamic stabilization lengths or segments 324 a and 324 b and one rigid length 328. At the segments 324 a and 324 b, respective slits 322 a and 322 b cooperate with the respective sleeves 310 a and 310 b. The core lengths or segments 324 a and 324 b and the slits 322 a and 322 b are similar or nearly identical to the core 8 and sleeve 10, respectively, previously described herein. However, the segment 324 a is integral with the segment 324 b and the segment 324 b is integral with the rigid length or segment 328. The flexible length 324 a that includes the slit 322 a is also integral or otherwise fixed to a shorter rigid length 326. In the illustrated embodiment, the length 326 is sized and shaped to be received by a receiver 31 of one of the bone screw assemblies 25 while the length 328 is elongate, of solid construction and sized to cooperate with at least two bone screw assemblies 25. The length 328 may be used in conjunction with spinal fusion. The sleeves 310 a and 310 b each include respective grooves 368 a and 368 b that are the same or substantially similar to the grooves 68 previously described herein with respect to the sleeve 10. Also, in the illustrated embodiment, the portion 326 is substantially similar or identical to the end portion 16 previously described herein with respect to the core 8. It is noted that the portion 326 may also be elongate, similar to the length 328, for cooperating with more than one bone screw assembly 25.

Thus the assembly 301 according to the invention is used to provide protected movement of the spine along both the segments 324 a and 325 b and rigid support along the length 328. In the illustrated embodiment, the portions or segments 324 a, 324 b, 326 and 328 are integral and substantially uniform along a central longitudinal axis D thereof, and are cylindrical. The segments 324 a, 324 b, 326 and 328 are also of solid construction with the exception of the portions of the segments 324 a and 324 b that have the respective helical slits 322 a and 322 b. As indicated above, the helical slits 322 a and 322 b are substantially similar or identical to the helical slit 22 previously described herein, having features and cross-sections as shown in FIGS. 3, 4 and 5.

In use, the assembly 301 is implanted in a manner substantially similar to that previously described herein with respect to the assembly 1. As with the assembly 1, if desired, during tightening of the closure structures 27 against the core 308, one or both of the sleeves 310 a and 310 b may be compressed between facing bone screw receivers 31 as previously described herein with respect to the sleeve 10.

It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown. 

1. In a medical implant assembly having at least two bone attachment structures cooperating with a longitudinal connecting member, the improvement wherein the longitudinal connecting member comprises: a) an inner core having a periphery and a slit formed into a portion of the periphery, the core being integral along an entire length of the connecting member; and b) an outer sleeve covering the slit, the sleeve disposed outside of the periphery, allowing respective freedom of movement between the inner core and the outer sleeve.
 2. The improvement of claim 1 wherein the slit is a helical slit disposed on a portion of the inner core and positioned between the at least two bone attachment structures.
 3. The improvement of claim 1 wherein the sleeve extends between and makes contact with the at least two bone attachment structures.
 4. The improvement of claim 3 wherein the sleeve is compressed during installation.
 5. The improvement of claim 1 wherein the core is cylindrical.
 6. The improvement of claim 1 wherein the sleeve has an external surface with at least one groove formed in the surface.
 7. The improvement of claim 1 wherein the sleeve has a cylindrical external surface with at least one and up to a plurality of compression grooves formed thereon.
 8. The improvement of claim 1 wherein the inner core has a first longitudinal section and an integral second longitudinal section, the first longitudinal section having the slit, the first longitudinal section extending between first and second bone attachment structures and the second longitudinal section extending between the second bone attachment structure and a third bone attachment structure.
 9. The improvement of claim 8 wherein the second longitudinal section has a second slit.
 10. The improvement of claim 8 wherein the second longitudinal section is a solid rod.
 11. The improvement of claim 8 wherein the inner core member has a third longitudinal section extending between the third bone attachment structure and a fourth bone attachment structure.
 12. In a medical implant assembly having at least first and second bone anchors cooperating with a longitudinal connecting member, the improvement wherein the connecting member comprises: a) an elongate bar of one-piece construction, the bar attachable to the at least first and second bone anchors, the bar having a slitted portion; and b) an outer sleeve disposed over the slitted portion and being slidable with respect to the slitted portion.
 13. The improvement of claim 12 wherein the bar is substantially solid.
 14. The improvement of claim 13 wherein the slitted portion is a substantially helical slit formed in the substantially solid bar.
 15. The improvement of claim 12 wherein the bar is substantially cylindrical.
 16. A longitudinal connecting member for cooperation with at least two bone anchors of a medical implant assembly, the member comprising: a) a substantially solid bar of one-piece construction having first and second ends and a helical slit formed on a portion of the bar spaced from both the first and second ends; and b) an elastic sleeve having a through bore, the bar receivable in the bore and freely slidable with respect to the sleeve, the sleeve being positioned over the bar portion having the helical slit, the sleeve being in contact with each of the at least two bone anchors. 